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Register a new userThe effects of peculiar velocities in SN Ia environments on the local $H_0$ measurement
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The discrepancy between estimates of the Hubble Constant ($H_0$) measured from local ($z lesssim 0.1$) scales and from scales of the sound horizon is a crucial problem in modern cosmology. Peculiar velocities ($v_{pec}$) of standard candle distance indicators can systematically affect local $H_0$ measurements. We here use 2MRS galaxies to measure the local galaxy density field, finding a notable $z$ < 0.05 under-density in the SGC-6dFGS region of 27 $pm$ 2 %. However, no strong evidence for a Local Void pertaining to the full 2MRS sky coverage is found. Galaxy densities are used to measure a density parameter, $Delta phi_{+-}$, which we introduce as a proxy for $v_{pec}$ which quantifies density gradients along a SN line-of-sight. $Delta phi_{+-}$ is found to correlate with local $H_0$ estimates from 88 Pantheon SNeIa (0.02 < $z$ < 0.05). Density structures on scales of $sim$ 50 Mpc are found to correlate strongest with $H_0$ estimates in both the observational data and in mock data from the MDPL2-Galacticus simulation. Using trends of $H_0$ with $Delta phi_{+-}$, we can correct for the effects of density structure on local $H_0$ estimates, even in the presence of biased $v_{pec}$. However, the difference in the inferred $H_0$ estimate with and without the peculiar velocity correction is limited to < 0.1 %. We conclude that accounting for environmentally-induced peculiar velocities of SNIa host galaxies does not resolve the tension between local and CMB-derived $H_0$ estimates.
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When measuring the value of the Hubble parameter, $H_0$, it is necessary to know the recession velocity free of the effects of peculiar velocities. In this work, we study different models of peculiar velocity in the local Universe. In particular, we compare models based on density reconstruction from galaxy redshift surveys and kernel smoothing of peculiar velocity data. The velocity field from the density reconstruction is obtained using the 2M++ galaxy redshift compilation, which is compared to two adaptive kernel-smoothed velocity fields: the first obtained from the 6dF Fundamental Plane sample and the other using a Tully-Fisher catalogue obtained by combining SFI++ and 2MTF. We highlight that smoothed velocity fields should be rescaled to obtain unbiased velocity estimates. Comparing the predictions of these models to the observations from a few test sets of peculiar velocity data, obtained from the Second Amendment Supernovae catalogue and the Tully-Fisher catalogues, we find that 2M++ reconstruction provides a better model of the peculiar velocity in the local Universe than the kernel-smoothed peculiar velocity models. We study the impact of peculiar velocities on the measurement of $H_0$ from gravitational waves and megamasers. In doing so, we introduce a probabilistic framework to marginalize over the peculiar velocity corrections along the line-of-sight. For the megamasers, we find $H_0 = 69^{+2.9}_{-2.8}$ km s^{-1} Mpc^{-1} using the 2M++ velocity field. We also study the peculiar velocity of the the galaxy NGC1052-DF2, concluding that a short $sim$ 13 Mpc distance is not a likely explanation of the anomalously low dark matter fraction of that galaxy.
Type Ia Supernovae (SNe Ia) are widely used to measure the expansion of the Universe. To perform such measurements the luminosity and cosmological redshift ($z$) of the SNe Ia have to be determined. The uncertainty on $z$ includes an unknown peculiar velocity, which can be very large for SNe Ia in the virialized cores of massive clusters. We determine which SNe Ia exploded in galaxy clusters. We then study how the correction for peculiar velocities of host galaxies inside the clusters improves the Hubble residuals. Using 145 SNe Ia from the Nearby Supernova Factory we found 11 candidates for membership in clusters. To estimate the redshift of a cluster we applied the bi-weight technique. Then, we use the galaxy cluster redshift instead of the host galaxy redshift to construct the Hubble diagram. For SNe Ia inside galaxy clusters the dispersion around the Hubble diagram when peculiar velocities are taken into account is smaller in comparison with a case without peculiar velocity correction, with a $wRMS=0.130pm0.038$ mag instead of $wRMS=0.137pm0.036$ mag. The significance of this improvement is 3.58 $sigma$. If we remove the very nearby Virgo cluster member SN2006X ($z<0.01$) from the analysis, the significance decreases to 1.34 $sigma$. The peculiar velocity correction is found to be highest for the SNe Ia hosted by blue spiral galaxies, with high local specific star formation rate and smaller stellar mass, seemingly counter to what might be expected given the heavy concentration of old, massive elliptical galaxies in clusters. As expected, the Hubble residuals of SNe Ia associated with massive galaxy clusters improve when the cluster redshift is taken as the cosmological redshift of the SN. This fact has to be taken into account in future cosmological analyses in order to achieve higher accuracy for cosmological redshift measurements. Here we provide an approach to do so.
How do peculiar velocities affect observed voids? To answer this question we use the VIDE toolkit to identify voids in mock galaxy populations embedded within an N-body simulation both with and without peculiar velocities included. We compare the resulting void populations to assess the impact on void properties. We find that void abundances and spherically-averaged radial density profiles are mildly affected by peculiar velocities. However, peculiar velocities can distort by up to 10% the shapes for a particular subset of voids depending on the void size and density contrast, which can lead to increased variance in Alcock-Paczynski test. We offer guidelines for performing optimal cuts on the void catalogue to reduce this variance by removing the most severely affected voids while preserving the unaffected ones. In addition, since this shape distortion is largely limited to the line of sight, we show that the void radii are only affected at the $sim$ 10% level and the macrocenter positions at the $sim$ 20% (even before performing cuts), meaning that cosmological probes based on the Integrated Sachs-Wolfe and gravitational lensing are not severely impacted by peculiar velocities.
We quantify the effect of supernova Type Ia peculiar velocities on the derivation of cosmological parameters. The published distant and local Ia SNe used for the Supernova Legacy Survey first-year cosmology report form the sample for this study. While previous work has assumed that the local SNe are at rest in the CMB frame (the No Flow assumption), we test this assumption by applying peculiar velocity corrections to the local SNe using three different flow models. The models are based on the IRAS PSCz galaxy redshift survey, have varying beta = Omega_m^0.6/b, and reproduce the Local Group motion in the CMB frame. These datasets are then fit for w, Omega_m, and Omega_Lambda using flatness or LambdaCDM and a BAO prior. The chi^2 statistic is used to examine the effect of the velocity corrections on the quality of the fits. The most favored model is the beta=0.5 model, which produces a fit significantly better than the No Flow assumption, consistent with previous peculiar velocity studies. By comparing the No Flow assumption with the favored models we derive the largest potential systematic error in w caused by ignoring peculiar velocities to be Delta w = +0.04. For Omega_Lambda, the potential error is Delta Omega_Lambda = -0.04 and for Omega_m, the potential error is Delta Omega_m < +0.01. The favored flow model (beta=0.5) produces the following cosmological parameters: w = -1.08 (+0.09,-0.08), Omega_m = 0.27 (+0.02,-0.02) assuming a flat cosmology, and Omega_Lambda = 0.80 (+0.08,-0.07) and Omega_m = 0.27 (+0.02,-0.02) for a w = -1 (LambdaCDM) cosmology.
It is known that the large-scale structure (LSS) mapped by a galaxy redshift survey is subject to distortions by the galaxies peculiar velocities. Besides the signatures generated in common N-point statistics, such as the anisotropy in the galaxy 2-pt correlation function, the peculiar velocities also induce distinct features in LSSs morphological properties, which are fully described by four Minkowski functionals (MFs), i.e., the volume, surface area, mean curvature and Euler characteristic (or genus). In this work, by using large suite of N-body simulations, we present and analyze these important features in the MFs of LSS on both (quasi-)linear and non-linear scales. With a focus on non-linear scale, we identify the features uniquely induced by the fingers-of-God effect that show up only on non-linear scales, especially in the surface-area weighted mean curvature in high density threshold regions. We also find the MFs may give competitive constraints on cosmological parameters compared to the power spectrum. These results are important for cosmological applications of MFs of LSS, and probablly open up a new way to study the peculiar velocity field itself.
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